1. Field of the Invention
The present invention relates to a magnetic head including a read head unit, a write head unit and two contact sensors.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system in which signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a main pole. The main pole has an end face located in a medium facing surface facing a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole passes therethrough a magnetic flux corresponding to the magnetic field produced by the coil, and produces a write magnetic field from its end face.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically in the form of a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of a recording medium by means of an airflow that comes from the leading end into the space between the medium facing surface and the recording medium.
It is demanded of magnetic disk drives that the distance between the medium facing surface and the recording medium be reduced for higher recording densities. To meet the demand, a magnetic head including a heater has been proposed, as disclosed in U.S. Patent Application Publication Nos. 2009/0251828 A1 and 2012/0218662 A1, for example. The magnetic head including the heater is configured so that part of the magnetic head expands with heat generated by the heater, and part of the medium facing surface thereby protrudes. This allows for a reduction in the distance between the medium facing surface and the recording medium.
For the magnetic head described above, the distance between the medium facing surface and the recording medium is controlled in the following manner, for example. First, before shipment of a magnetic disk drive as a final product, the following test is performed. In the test, with the slider floated above the surface of a rotating recording medium, the magnitude of the power being supplied to the heater is gradually increased to gradually increase the amount of protrusion of part of the medium facing surface. Then, the magnitude of the supply power to the heater at which the part of the medium facing surface comes into contact with the recording medium is determined. Such magnitude of the supply power will be referred to as “power at contact”. At the time of shipment of the magnetic disk drive as a final product, the magnitude of the supply power to the heater is set to a predetermined value smaller than the power at contact. The distance between the medium facing surface and the recording medium is recognized and controlled by the magnitude of the supply power to the heater.
To control the distance between the medium facing surface and the recording medium in the above-described manner, it is necessary to detect contact of part of the medium facing surface with the recording medium in the foregoing test. The magnetic head disclosed in U.S. Patent Application Publication No. 2012/0218662 A1 includes a contact sensor for detecting contact of part of the medium facing surface with the recording medium. For this magnetic head, it is thus possible to detect contact of part of the medium facing surface with the recording medium through the use of the contact sensor.
For magnetic heads to achieve desired read and write characteristics suitable for high recording densities, it is desirable that the distance between the read head unit and the recording medium and the distance between the write head unit and the recording medium be adjusted to respective desired small values.
The magnetic head disclosed in U.S. Patent Application Publication No. 2009/0251828 A1 includes two heaters: one for causing a read sensor to protrude; and the other for causing a main pole layer to protrude. In this magnetic head, the amount of protrusion of the read sensor and the amount of protrusion of the main pole layer can be controlled independently of each other. However, it is impossible with this magnetic head to know how much amount of protrusion of the read sensor will bring the read sensor into contact with the recording medium and how much amount of protrusion of the main pole layer will bring the main pole layer into contact with the recording medium. It is thus difficult with this magnetic head to recognize and control the distance between the read sensor and the recording medium and the distance between the main pole layer and the recording medium during actual use.
For the magnetic head disclosed in U.S. Patent Application Publication No. 2012/0218662 A1, it is possible to detect contact of part of the medium facing surface with the recording medium through the use of the contact sensor, as mentioned above. In this magnetic head, however, a contact of part of the medium facing surface with the recording medium will not always bring both of the read head unit and the write head unit into contact with the recording medium, and it is thus impossible to know the relative positions of the read head unit and the write head unit with respect to the recording medium when part of the medium facing surface is in contact with the recording medium. Consequently, even if the foregoing test is performed before shipment of the magnetic disk drive as a final product, it is difficult with this magnetic head to recognize and control the distance between the read head unit and the recording medium and the distance between the write head unit and the recording medium during actual use.